A new book is being published this week of personal letters written by Mother Teresa -- the Roman Catholic nun who won the Nobel Peace prize in 1979 for her humanitarian work in India. The letters show that during her spiritual life, Mother Teresa suffered a crisis of faith and a sense of being abandoned by Jesus Christ. Sabina Castelfranco spoke to the book's editor and has this report from Rome.

Mother Teresa's dark years of the soul had not been made public until now. The nun's struggle with doubts about her faith is evident in her private letters when she wrote of feeling "a terrible darkness within me."

Father Brian Kolodiejchuk edited the book, titled: Come Be My Light: The Private Writings of the 'Saint of Calcutta’, which will be published in English this week. He knew Mother Teresa for 20 years. "The whole book is," he explains, "as it were, a commentary on what I call Mother Teresa's mission statement: if I ever become a saint I will be a saint of darkness. I'll be absent from heaven, lighting the light of those in darkness on earth."

Mother Teresa was known as the "saint of the gutters". She ministered to the needs of the poor, sick, orphaned, and dying in Calcutta, India for more than 40 years. In 1979, she won the Nobel Peace Prize for her humanitarian work.

Father Brian says her work was tireless. "She really did give and she was always really focused on the other and (had) very little or hardly any personal time."

Father Brian has been promoting Mother Teresa's cause for sainthood. He does not believe the letters will jeopardize her chances of becoming a saint. He says her writings show moments of uncertainty and discouragement. But they also tell us something more about this very special nun's spiritual life. "This sense of surrendering oneself and abandoning oneself to God no matter what one is feeling -- that is something we have heard, but to see her actually have done it in such painful circumstances is certainly a surprise and very moving. Some of the letters you read are very powerful."

Those who were close to Mother Teresa insist her inner suffering should not be seen as a denial of God. Father Brian argues that the nun's faith always remained, but that she struggled because she could not feel Him.

Mother Teresa was put on a fast-track to sainthood by Pope John Paul II and beatified in 2003 just six years after her death. Now an additional miracle, recognized by the Vatican, is required for her to become a saint.